Currently, circuit switching technology forms the basis for the world-wide telecommunications network infrastructure and is used extensively in telephone systems, however the recent expansion of the Internet has fueled the use of packet-based technologies. Packet-based technologies can be used as an alternative or in combination with circuit switching technologies in these telecommunications networks and telephone systems. When packet-based and circuit-based communication technologies are used together, a bridge, known as a gateway, is necessary to transform and route signals between a circuit network and a packet network. Telephony gateways interconnecting to the circuit network may use standards-based time division multiplexed (TDM) trunks (T1, T3, E1, etc) and standards-based signaling mechanisms (e.g., Signaling System 7 or channel associated signaling). An example of a circuit network is the telephone system that provides subscribers with plain old telephone service (POTS). The gateway may interconnect to the packet network through standards-based packet interfaces such as Internet Protocol (IP), Frame Relay and Asynchronous Transfer Mode (ATM) over a variety of physical interfaces (e.g., 100 BaseT, T3, OC3c, OC12c). An example of a packet network is the Internet.
FIG. 1 illustrates the architecture of a prior art telephony gateway 10. This gateway architecture uses a circuit switch fabric 12 such as a TDM bus or a Time-Slot-Interchange to provide the internal switching between the circuit network 14 and the packet network 16. Circuit-to-circuit calls, as indicated by line 15, are switched between circuit network servers 18 using the circuit switch fabric 12. Circuit-to-packet calls, as indicated by line 17, are switched between circuit network servers 18 and packet network servers 19 using this same circuit switch fabric 12. The conversion of the circuit data to packet data, which is known as packet adaptation, is performed in the packet network servers 19, which incorporate digital signal processors (not shown) for echo cancellation and transcoding. The circuit switch fabric 12, however, limits the overall flexibility of the gateway to move packets among server cards.
FIG. 2 illustrates the architecture of another prior art telephony gateway 20. For greater flexibility, this gateway architecture separates the signal processing functions from the packet network servers 22 and places these functions on signal processing servers 21. In addition, a packet switch fabric 23 allows connectivity from any signal processing server 21 to any packet network server 22. It is well known that a packet switch fabric 23 can be implemented with a variety of technologies, such as an arbitrated packet bus or a centralized switching module. As in the gateway architecture of FIG. 1, circuit-to-circuit calls are switched via the circuit switch fabric 12 as indicated by line 24. Circuit-to-packet calls, as indicated by line 25, are first switched by the circuit switch fabric 26 to a signal processing server 21 that contains an available digital signal processor (DSP) for performing signal processing. The signal processing server 21 uses the packet switch fabric 23 to move the processed information to a packet network server 22 and the associated packet network interface selected during call establishment. The separation of the signal processing function on separate servers allows a call-by-call selection of different DSP-based functions. For example, different calls can use different compression algorithms, with differing processing complexity, residing on different signal processing servers 22. While the flexibility of the packet switch fabric 23 represents an improvement over the architecture of FIG. 1, the architecture of FIG. 2 carries the cost and complexity burden of two separate and independent switch fabrics: one circuit and one packet.